The present invention relates to a method for testing intraocular lenses for the purpose of determining the quality thereof. In particular, the method of the present invention is directed to the use of a nullifying lens in the testing of multifocal intraocular lenses and in the testing of intraocular lenses having designed-in optical aberrations. The invention is further directed to a nullifying lens configured such that light passing through an intraocular lens and through the nullifying lens is focused at a single plane, thereby facilitating an analysis of the optical characteristics of the intraocular lens.
U.S. Pat. No. 4,213,701 to Lanzilloti discloses a method and apparatus for testing intraocular lenses. In particular, Lanzilloti discloses an apparatus constructed for use in determining the dioptric power, resolving power, and astigmatic power of an intraocular lens. U.S. Pat. No. 4,639,133 to Cole also discloses a method for determining the dioptric power of an intraocular lens. However, neither Lanzilloti nor Cole addresses the issue of quality testing of multifocal intraocular lenses and intraocular lenses having designed-in optical aberrations.
The U.S. Food and Drug Administration (FDA) requires that all multifocal intraocular lenses be subjected to a series of qualitative and quantitative analyses for the purpose of determining whether each lens meets the requisite optical standards. These qualitative analyses include a determination of the lens' resolution, resolution efficiency, and modulation transfer function (MTF).
Due to the presence of multiple optical zones or designed-in aberrations in certain intraocular lenses, it can be difficult to fulfill the above-referenced FDA testing requirements. For example, multifocal intraocular lenses include a plurality of zones having different optical characteristics, including different focal lengths. Thus, light directed through these multifocal intraocular lenses will have a plurality of focal points. Although it is possible to conduct separate analyses of the multifocal intraocular lens at each of these focal points, such a testing procedure is time-consuming and does not provide sensitive results. The lack of sensitivity associated with such testing procedures is caused by the fact that light focused by one optical zone of the multifocal lens will tend to be blurred by light refracted by other zones of the lens which are not designed to focus an image at the same plane, thereby making an accurate analysis difficult or impossible. As a result, the detection of fabrication defects in multifocal intraocular lenses using standard testing techniques is not particularly practical using known testing procedures. The same problem also exists with respect to intraocular lenses having designed-in optical aberrations.